1. Field of the Invention
The present invention relates to a printed circuit board, more specifically to a printed circuit board that includes an electromagnetic bandgap structure and solves a mixed signal problem between an analog circuit and a digital circuit.
2. Background Art
Various apparatuses such as mobile communication terminals, personal digital assistants (PDA), laptop computers and digital multimedia broadcasting (DMB) devices have been launched in order to meet today's trend that mobility is considered as one of the most important issues.
Such apparatuses include a printed circuit board, which is configured to compound analog circuits (e.g. radio frequency (RF) circuits) and digital circuits for wireless communication.
FIG. 1 is a sectional view showing a printed circuit board including an analog circuit and a digital circuit. Although a 4-layered printed circuit board is illustrated, various printed circuit boards, such as 2- or 6-layered printed circuit boards, can be applied. Here, the analog circuit is assumed to be an RF circuit.
The printed circuit board 160 includes metal layers 110-1, 110-2, 110-3 and 110-4 (hereinafter, collectively referred to as 110), dielectric layers 120-1, 120-2 and 120-3 (hereinafter, collectively referred to as 120) stacked in between the metal layers 110, a digital circuit 130 mounted on the top metal layer 110-1 and an RF circuit 140.
If it is assumed that the metal layer represented by reference numeral 110-2 is a ground layer and the metal layer represented by reference numeral 110-3 is a power layer, a current passes through a via 160 connected between the ground layer 110-2 and the power layer 110-3 and the printed circuit board 100 performs a predetermined operation or function.
Here, an operation frequency of the digital circuit 130 and an electromagnetic (EM) wave 150 by harmonics components are transferred to the RF circuit 140, to thereby generate a problem of mixed signals. The mixed signal problem is generated due to the EM wave, having a frequency within the frequency band in which the RF circuit 140 is operated, in the digital circuit 130. This problem results in obstructing the accurate operation of the RF circuit 140. For example, when the RF circuit 140 receives a signal ranging a certain frequency band, transferring the EM wave 150 including the signals ranging the certain frequency band from the digital circuit 130 may make it difficult to accurately receive the signal ranging the certain frequency band.
Solving the mixed signal problem becomes more difficult due to the increased complexity of electronic apparatuses and the higher operation frequency of the digital circuit 130.
A decoupling capacitor, typical solution for the power noise, can not be a proper solution in high frequency, and study for a structure of blocking high frequency noise between the RF circuit and digital circuit is needed.